UVA 11475 Extend to Palindrome

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 #define clr(a,val) memset(a,val,sizeof(a))
 4 #define lowbit(x) x&-x
 5 #define eps 1e-6
 6 #define RI register int
 7 typedef long long ll;
 8 const int INF=0x3f3f3f3f;
 9 const int maxn=1e6+10;
10 string str,rev;
11 int nxt[maxn]; 
12 void getnext(string s)
13 {
14     nxt[0]=0;nxt[1]=0;
15     for(int i=1,len=s.length();i<len;++i)
16     {
17         int j=nxt[i];
18         while(j&&s[i]!=s[j]) j=nxt[j];
19         nxt[i+1]=s[i]==s[j]?j+1:0;
20     }
21 }
22 void solve()
23 {
24     int x=0,y=0,ans=0;
25     int len=str.length();
26     while(y<len)
27     {
28         if(rev[x]==str[y])
29         {
30             x++,y++;
31             ans=x;
32         }
33         else if(x>0) x=nxt[x];
34         else x=0,y++;
35     }
36     cout<<str<<rev.substr(ans)<<endl;
37 }
38 
39 int main()
40 {
41     while(cin>>str)
42     {
43         rev=str;
44         reverse(rev.begin(),rev.end());
45         getnext(rev);
46         solve();
47     }
48     
49     return 0;
50 }